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From "Rui Li (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-17486) Enable SharedWorkOptimizer in tez on HOS
Date Thu, 02 Nov 2017 08:43:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-17486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16235400#comment-16235400
] 

Rui Li commented on HIVE-17486:
-------------------------------

I also think that's possible in theory. But I guess it will require lots of work. E.g. we
may need to modify MapOperator to accommodate the new M->M->R scheme. I'm wondering
whether it'll be easier to find a way to cache equivalent MapInput. I noted the caching was
disabled by HIVE-8920. [~xuefuz] do you still remember the reason why it was disabled?

> Enable SharedWorkOptimizer in tez on HOS
> ----------------------------------------
>
>                 Key: HIVE-17486
>                 URL: https://issues.apache.org/jira/browse/HIVE-17486
>             Project: Hive
>          Issue Type: Bug
>            Reporter: liyunzhang
>            Assignee: liyunzhang
>            Priority: Major
>         Attachments: scanshare.after.svg, scanshare.before.svg
>
>
> in HIVE-16602, Implement shared scans with Tez.
> Given a query plan, the goal is to identify scans on input tables that can be merged
so the data is read only once. Optimization will be carried out at the physical level.  In
Hive on Spark, it caches the result of spark work if the spark work is used by more than 1
child spark work. After sharedWorkOptimizer is enabled in physical plan in HoS, the identical
table scans are merged to 1 table scan. This result of table scan will be used by more 1 child
spark work. Thus we need not do the same computation because of cache mechanism.



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